Hi Darrel,
Nope, the Kalman filter (if I ever understand/get that to work) would be used only to track the absolute angle of the robot platform. (Basicly removing the gyro drift). The error (desired angle - actual angle) is then fed to the PID-filter which in turn tells the motor-driver how fast the wheels needs to spin to keep it upright (or whatever).

As it stands at the moment (with the SHARP sensors) it just subtract the front sensor reading from the rear sensor reading and sends that value the PID-filter.

Thanks

/Henrik Olsson.